To manufacture a thin disk such as a semiconductor wafer, an elongated billet of semiconductor material is cut into very thin slices or disks, about ½ mm in thickness. The slices or wafers of semiconductor material are then lapped and polished by a process that applies an abrasive slurry to the wafer's surfaces. After polishing, slurry residue conventionally is cleaned or scrubbed from wafer surfaces via a mechanical scrubbing device, such as a device which employs polyvinyl acetate (PVA) brushes, brushes made from other porous or sponge-like material, or brushes having bristles made from nylon or similar materials. Although these conventional cleaning devices remove a substantial portion of the slurry residue which adheres to wafer edges, slurry particles nonetheless may remain and produce defects during subsequent processing.
A conventional PVA brush scrubber is shown in the side elevational view of FIG. 1. The conventional scrubber 11, shown in FIG. 1, comprises a pair of PVA brushes 13a, 13b, a platform 15 for supporting a wafer W, and a mechanism (not shown) for rotating the pair of PVA brushes 13a, 13b. The platform 15 comprises a plurality of rollers 17a-c for both supporting and rotating the wafer W.
Preferably, the pair of PVA brushes 13a, 13b are positioned to extend beyond the edge of the wafer W, so as to facilitate cleaning the wafer's edge. However, research shows that slurry induced defects still occur, and are caused by slurry residue remaining along the edges of the wafer despite cleaning with apparatuses such as that described above. Specifically, subsequent processing has been found to redistribute slurry residue from the wafer edges to the front of the wafer, causing defects.
A number of devices have been developed to improve wafer edge cleaning. One such device is shown in the side elevational view of FIG. 2. The edge-cleaning scrubber 19, shown in FIG. 2, includes a pair of rollers 17b, 17c adapted to support and rotate the wafer W, and further includes an edge-cleaning roller 21 that fits over the edge of the wafer W for cleaning the edge as the wafer rotates. Although the edge-cleaning roller 21 addresses the need to clean slurry residue from wafer edges, it can be subject to quick wear, such wear typically being concentrated at locations where it contacts the wafer W.
FIGS. 3A-3C illustrate details related to how the edge-cleaning roller 21 of the edge-cleaning scrubber 19 of FIG. 2 cleans the edge of the wafer W. Referring to the side elevational view of FIG. 3A, which shows the wafer W above the edge-cleaning roller 21, the edge-cleaning roller 21 of FIG. 2 is shown in contact with the wafer W. Specifically, opposing first and second inclined surfaces 23, 25 of the edge-cleaning roller 21 are in contact with respective opposite first and second edge corners 27, 29 of the edge of the wafer W. For example, either or both of the first and second edge corners 27, 29 may comprise a bevel so as to form, e.g., a truncated frustoconical edge surface (not separately shown) which may be placed in surface-to-surface contact with the first and second inclined surfaces 23, 25 of the edge cleaning roller 21.
Referring to the side elevational view of FIG. 3B, in which the wafer W is shown in phantom across the edge-cleaning roller 21, the wafer W rotates in a nominal rotation plane 31, as does the edge-cleaning roller 21. By “nominal rotation plane” is meant that plane within which the wafer W is expected to rotate based on the specific arrangement of rollers (e.g., the rollers 17b, 17c) used to support, drive and guide the wafer W within the edge-cleaning scrubber 19 of FIG. 2. Further, it may be seen that contact between inclined surfaces 23, 25 of the edge-cleaning roller 21 and the first and second edge corners 27, 29 of the wafer W takes place along respective first and second contact areas 33, 35 on the inclined surfaces 23, 25.
Referring to the cross-sectional view of the edge-cleaning roller 21 shown in FIG. 3C, corresponding to section 3C-3C as shown on FIG. 3B, the first contact area 33 on the first inclined surface 23 translates to a ring-shaped wear sector 37 on the first inclined surface 23, typically relatively narrow, which performs the edge-cleaning function and is subject to friction-induced wear over time. Conversely, the remaining portions of the first inclined surface 23 may not typically contact the wafer W during edge cleaning, and therefore may not be subject to such friction-induced wear.
Other rollers that may rotate in a common plane with a wafer W while contacting a portion of the wafer edge, but that perform additional or separate functions such as rotating the wafer W (e.g., drive rollers, such as the spinning mechanism 17a-c of FIG. 1) or guiding the rotating wafer W so as to limit or prevent tilting of the same (e.g., idling guide rollers (not separately shown)), are typically also subject to rapid wear where contact is made with the wafer W. The cost of maintaining proper operation of such parts and/or conducting frequent replacement of the same can mount quickly.
Accordingly the field of wafer cleaning requires methods and apparatus for effectively performing one or more of the functions of cleaning, supporting, driving and guiding both the flat surfaces and the edge surfaces of a semiconductor wafer, preferably so as to reduce the cost and/or frequency of replacement due to frictional wear from wafer contact.